Best advice I can give you is to go to Amazon and purchase "How to Print T-Shirts for Fun and Profit" by Scott Fresener. (Just don't buy one of his DTG printers... but that's another story).
"THE BOOK" will tell you everything you need to know about screen printing, and even gives plans for building your own press (that's how I started out). After you read the book, find out if there's a trade show in a nearby state coming up, and spend the money to go and take every seminar they offer, and walk the show floor and talk to other people there. Only after that should you start investing in equipment and supplies. The first two pieces of equipment you have to have are a press (even a cheap one-screen press) and a flash cure unit (which you can use to cure for a while). You can start out exposing your screens in the sunlight (clumsy, but it will work for one-color images to get started). Get a few screens (110 count and 155 count mesh to start), a couple of quarts of basic plastisol ink colors (black, red, white, blue and yellow are good to start -- you can mix green, orange, purple and brown), a squeegee, emulsion and quart sizes of cleaning and reclaiming chemicals. If you like it and find yourself eager to keep going, you can start adding more equipment. If you hate it, you aren't out too much (the flash cure unit is the biggest expense).
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